Engaging in physical activity is one of the most important health habits known to contribute to a variety of positive health outcomes, including longevity, increased quality of life and levels of daily functioning, and reduced rates of diabetes and obesity. This study capitalizes on an already existing community participatory infrastructure (Park Advisory Boards), and a collaborative relationship between RAND, the City of Los Angeles Department of Recreation and Parks, and a community-based organization, the Multi-cultural Area Health Education Center (MAHEC). We will conduct a randomized controlled intervention trial in which 25 parks will be randomized to a CBPR condition involving their boards and local communities in research: park assessments, data analysis and interpretation to inform use of discretionary funds for programming and facilities, while 25 other parks will be randomized to a control condition and will not be involved in the research assessments, but will have findings on park utilization given to administrators to act on. Our overall study goals are to examine how public parks influence physical activity, and to determine whether population level physical activity can be enhanced through involving communities in scientific and systematic park assessments to guide modification of park programs and facilities. Our specific aims include: 1. to describe how different age, gender, and racial/ethnic groups use local parks and identify park characteristics and programs that promote moderate-vigorous physical activity. 2. To compare the efficacy of involving park advisory boards and other community members in the research process (CBPR) in affecting park programming and thereby promoting increased population level physical activity, versus merely providing assessment data to park directors (top down approach). Our methods will include a pre-post design with assessments at baseline, and 1 year, the use of direct observation with SOPARC (Systematic Observation of Parks and recreation in Communities), intercept surveys of park users and randomly selected household surveys. Not only will this study further our understanding of the role of parks in physical activity and health, but it will also be the first randomized trial of the CBPR process to see whether it is more effective in successfully implementing programs that better serve community needs than traditional top-down approaches.